I have an Iphone 4 with 5.1.1 shsh blobs on file with cydia (never went higher). Never did OTA update. Still have unlockable baseband (only pwnagetool used in the past).

Here's my question - I want to clean this phone off with a clean 5.1.1 jailbreak and unlock before selling it off. What's the best way to do this? Which tool do I need and do I need to do something special now that 5.1.1 is no longer unsigned? Is there a good guide out there for this situation?